The instant invention relates to time-of-day watt-hour meters, and, more particularly, to a time-of-day watt-hour meter having a variable sensitivity controlled from a central control station.
The energy shortage has caused greatly increased interest by electric utilities in "time-of-day" metering, i.e., charging the customer a higher rate per kilowatt-hour during predetermined and announced daily periods of peak energy use. For example, for many utilities peak consumption occurs during several hours in the early evening. Time-of-day metering is attractive as an inducement to customers to use less electricity during those peak hours, which would allow the utility to save money and fuel by not having to invest in expensive and little-used peak generating capacity. The customer is given an economic incentive to operate electrical appliances at the lower cost time.
Conventional time-of-day watt-hour meters have two or more sets of read-out dials, one set which reads power consumption during the normal periods, and one (or more) set that reads power consumption during the high cost period (or periods). The switching between the sets of dials is done by an electric clock or electric timer. In some time-of-day meters this clock controls a solenoid, which shifts gears to connect the rotor of the watt-hour meter to one or the other set of output dials. Alternatively, magnetic clutches or brakes can be used to couple the induction rotor to the appropriate output registers. Other prior art time-of-day meters consist of two complete watt-hour meters in one case, each connected to its own set of dials. A timer shifts from one meter to the other by switching an electrical contact, e.g., energizing the voltage coil of one or the other meter to record the kilowatt hours used during the specified time period.
These prior art time-of-day meters allow only two or a very limited number of separate metering periods, and when an interruption in power delivery to a customer occurs, the clock which controls the energization of the selected meters must be adjusted to correct for the period of power outage. This adds greatly to the cost of time-of-day metering in terms of both the meter itself incorporating the clock and the multiple read-outs and in personnel cost to ensure appropriate settings of the necessary clocks. Another limitation of conventional time-of-day meters is that they lack flexibility, i.e., the electric utility may wish to shift the "high-cost" hours to accommodate differences in summer/winter peaks or to omit weekends and holidays. Also, the annual shift to daylight-savings hours complicates time-of-day metering. Thus, either the timer in the conventional time-of-day meter has to be very complex, or else utility personnel have to go around and reset thousands of timers at least several times a year.